It is known practice to use collagen products prepared from animal tissues in medicine for treating wounds and for filling pathological cavities in bones. Collagen products of this type are described e.g. in the following patents: British Pat. No. 1,147,072, South African Pat. No. 6,705,871, U.S. Pat. No. 4,016,877, U.S. Pat. No. 3,823,212, U.S. Pat. No. 3,810,473 and U.S. Pat. No. 4,066,083 (P. Ries).
The process described in U.S. Pat. No. 4,066,083 comprises comminuting collagen-containing animal tissues at a temperature not exceeding 40.degree. C., degreasing the resulting tissue pulp and simultaneously removing therefrom undesirable water-soluble non-collagen ballast substances by repeatedly treating the tissue pulp with about a five-fold volume, based on the pulp volume, of a 5 to 15% aqueous sodium chloride solution containing about 0.2 to 1 part by weight of sodium azide as a preserving agent per 1000 parts by weight of the said solution and 0.5 to 2% by weight of a non-ionic fat-dispersing wetting agent, washing the resulting fiber pulp with water or 0.1 to 0.5% aqueous formic, acetic or citric acid, digesting the fiber pulp for 8 to 48 hours at a pH of about 2.5 to 3.5 in a five-fold volume, based on the volume of the pulp, of 0.1 to 5% aqueous acetic acid containing about 1 part by weight of pepsin per 1000 parts by weight of the tissue used as the starting material in order to remove non-collagen type proteins and telopeptides, precipitating collagen from the resulting collagen suspension by the addition thereto of aqueous sodium chloride in such a quantity that the sodium chloride concentration of the suspension is about 3 to 5%, separating the precipitated collagen and desalting it by ultrafiltration, dialysis or washing with 60 to 75% aqueous ethyl alcohol, dissolving the desalted collagen in demineralized or distilled water containing up to 3% by weight of a strong organic acid in such a proportion that the concentration of collagen in the resulting solution corresponds to a dry residue of about 0.5 to 2% by weight, freeze-drying the collagen solution, and sterilizing the freeze-dried collagen product.
The collagen product obtained by this process possesses a number of advantageous properties which appear to make it particularly suitable as an auxiliary material in medicine, but has the disadvantage that it is slow in taking up aqueous solutions or body fluids and has insufficient mechanical strength in moist or wet condition.